Currently, regarding a requirement for mobile communication, people demand more than telephony and messaging services. With rapid development of the Internet (the Internet), a large quantity of multimedia services have emerged, and some of application services may be implemented by receiving same data by multiple users, such as video on demand, television broadcasting, video conferencing, online education, and interactive gaming.
Compared with a common service, a mobile multimedia service features a large amount of data, long duration, latency sensitivity, and the like. A current IP (Internet Protocol) multicast technology is not applicable to a mobile network, because the mobile network has a specific network architecture, a specific function entity, and a unique radio interface bearer, which are different from those of a wired IP network. Consequently, an existing IP multicast technology cannot support sharing of a mobile network resource among multiple mobile users. Therefore, 3G mobile operators represented by Hutchison 3G (Hutchison, an operator in Hong Kong) actively seek a new service manner, which can implement broadcast of multimedia information and consume a relatively small quantity of system resources, so as to fulfill a purpose that operation of a traditional mobile service is not affected.
To implement that a mobile network resource is most effectively utilized, the 3GPP (a global standardization organization) has proposed an MBMS (multimedia multicast and broadcast service). The MBMS refers to a point-to-multipoint service in which one data source sends data to multiple users, which implements sharing of network resources, including a resource of a mobile core network, a resource of an access network, and especially an air interface resource. The MBMS defined by the 3GPP can not only implement pure-text, low-rate messaging-type multicast and broadcast, but also implement high-rate multimedia service multicast and broadcast, which undoubtedly follows a development tendency of a mobile data service in the future.
When UE (user equipment) detects that signal quality is relatively poor or that the UE needs to perform a handover because of another factor, the UE is first handed over from the MBMS to unicast, and then be handed over from an S-eNB (source base station) to a T-eNB (target base station), as shown in FIG. 1. Because the signal quality of the UE in the S-eNB is relatively poor, and there is a problem that unicast may not cover the UE, a failure is caused in establishing the unicast in the S-eNB, and it is hard to ensure service continuity.
Further, if the UE in the S-eNB receives a service by using a unicast bearer, though the UE in the T-eNB uses a multicast/multicast bearer to implement the service, when the UE is connected to the T-eNB and wants to use the multicast/multicast bearer to receive data, generally, service continuity cannot be ensured, either.